Rain gives pollution a break in Pune, Delhi, Mumbai

PUNE: Worsening pollution levels got a break this year, with Pune, Delhi, Mumbai and Ahmedabad witnessing a significant decline in pollutants PM 10 and PM 2.5 concentrations both in March and April 2023 as compared to the same period the previous year, SAFAR-IITM data showed, reports Neha Madaan.
SAFAR-IITM experts said the air quality in some of the major cities in India has been the best during the season since 2021, largely due to frequent rain spells received in many parts of the country. Delhi witnessed a 32% decrease in PM 10 concentration in March this year (135.5 g/m³) compared to the same period in 2022 (197.9 g/m³).
The national capital also saw a significant drop in this pollutant of nearly 33% in April this year (164.5 µg/ m3 ) in comparison to last April (247 µg/m3 ). PM 2.5 concentrations in Delhi reduced by 23% in March (62 µg/m3 ) and 33% in April (57.7 µg/m3 ) this year, in comparison to the same period last year (80 µg/m3 in March 2022 and 85.8 µg/m3 in April 2022).
Pune, too, saw a reduction in the pollution levels, with PM 10 concentrations dropping by 14% this March (92 µg/m3 ) compared to last March (107 µg/m3 ), and falling by 20% in April (77 µg/m3 ) compared to last year (96 µg/m3 ). PM 2.5 levels also dropped in the city over the last two months, to 57 µg/m3 in March and 44 µg/m3 in April this year.
Last year, these values were 65 µg/m3 in March and 58 µg/m3 in April. The trend was not limited to Delhi and Pune alone. Mumbai and Ahmedabad also saw similar drops in March and April this year. SAFAR-IITM experts attributed the reduction in pollution levels to the frequent rain spells received in many parts of India this season.
Rain plays a significant role in washing away pollutants, which is why the monsoon season has the least polluted air in India. A SAFAR-IITM scientist said, “One of the main ways by which rain spells can reduce pollution is by ‘washing away’ pollutants from the air and depositing them on the ground.
This process is known as wet deposition. It can help remove particulate matter and other pollutants from the atmosphere. Additionally, rain can help disperse pollutants by mixing them with air currents and diluting their concentration in the atmosphere.”
Another way that rain can help control pollution is by reducing the formation of secondary pollutants such as ozone. “When the atmosphere is dry, pollutants react with sunlight to form ozone, which can be harmful. When it rains, the moisture in the air helps reduce the amount of ozone that is formed,” the scientist said.
The SAFAR data, in this report, did not include ozone concentrations in these cities.